1. Field of the Invention
The present invention relates to printing methods and printing apparatuses.
2. Description of the Related Art
Inkjet printers (hereinafter referred to simply as “printers”) that eject ink onto paper serving as a medium to form dots are known as printing apparatuses for printing images. These printers repeat alternately a dot formation operation of forming dots on a paper by ejecting ink droplets from a plurality of nozzles which move together with a carriage, and a carrying operation of carrying the paper in an intersecting direction that intersects with the movement direction (hereinafter, referred to as the “carrying direction”) using a carry unit. By repeating these operations, raster lines are formed on the paper that consist of a plurality of dots arranged in the movement direction of the carriage. An image is printed by a plurality of the raster lines being formed in the carrying direction.
With this type of printer, the ink-droplet ejection characteristics, such as the amount of the ink droplet and the travel direction, vary from nozzle to nozzle. Such variations in the ejection characteristics are a cause of darkness non-uniformities in printed images, and thus are not preferable. Accordingly, with conventional methods, a correction value is set for each nozzle and the amount of ink is adjusted based on those correction values that are set (see JP H2-54676A for example).
In this conventional method, an output characteristics coefficient that indicates the characteristics of the ink ejection amount for each nozzle is stored in a head-characteristics register. Then, when an ink droplet is to be ejected, this output-characteristics coefficient is used to prevent darkness non-uniformities in the printed images.
However, the above-described conventional method corrects the ejection amount of ink droplets from each nozzle, but does not give consideration to darkness non-uniformities caused by the travel curve of ink droplets. Such darkness non-uniformities are related to landing positions of ink droplets ejected from the nozzles and are brought about by displacement in the carrying direction from the normal position. In other words, darkness non-uniformities occur when the spacing between adjacent raster lines becomes narrower or wider than the prescribed spacing. Accordingly, the darkness non-uniformities occur due to combinations of nozzles responsible for each raster line. For this reason, according to the conventional method described above, darkness non-uniformities due to the travel curve of ink droplets can occur when the sequence of the nozzles that form each raster line is different from the arrangement of the nozzles in the heads.
For example, there are cases where darkness non-uniformities can occur when using the interlaced mode as the print mode. The interlaced mode is a print mode in which unformed raster lines are set between raster lines that are formed in a single dot formation operation, and all of the raster lines are formed in a complementary manner through a plurality of dot formation operations. With this print mode, adjacent raster lines are not printed by the same nozzle. With this interlaced mode, there are cases in which the sequence of the nozzles responsible for adjacent raster lines in a printed image differs from the arrangement of the nozzles in the head, and darkness non-uniformities due to the travel curve can occur in these cases. The occurrence of such darkness non-uniformities reduces the quality of the printed images.